1. Field of the Invention
The present invention relates to a node and a method of setting a backup path.
2. Description of the Related Art
For example, Generalized Multi-Protocol Label Switching (GMPLS) signaling Resource ReserVation Protocol-Traffic Engineering (RSVP-TE) Extensions (RFC3473) is cited as a typical technique for path-setting by using a signaling on Synchronous Optical Network (SONET) or Synchronous Digital Hierarchy (SDH) network.
Japanese Patent Laid-Open No. 2003-101558, for example, discloses a technique that a working path and a backup path are set at the same time by a signaling on Uni-Directional Path Switched Ring (UPSR), i.e., a single ring type of SONET or SDH network. In this technique, a transmitting node transmits two signals towards a receiving node via two different paths on the ring. In other words, the transmitting node transmits one signal via one path and other signal via other path. A path switch included in the receiving node selects one of the two paths as a working path so that the other path automatically becomes a backup path.
Some networks, however, include a plurality of rings (hereinafter, “multiple-ring network”), and adjacent rings in such networks are connected via two or more paths. In such multiple-ring networks, with the conventional technique of setting a working path and a backup path by signaling, it is not possible to select a backup path and a working path at the same time from among the more than two paths existing between a transmitting node and a reception node.
Namely, RSVP-TE Extensions relates to setting paths by signaling, however, it is not define a method of setting a backup path at the same time while a working path is set by the signaling. Japanese Patent Laid-Open No. 2003-101558 discloses a method of setting a working path and a backup path in a single ring network, however, does not teach a method of setting a working path and a backup path at the same time in a multiple-ring network.
Japanese Patent Application No. 2005-209961 discloses a technique of setting a backup path at the same time as a working path in a multiple-ring network.
Specifically, in the technique disclosed in Japanese Patent Application No. 2005-209961, each of nodes composing a ring stores therein a list of the nodes (topology information of the nodes in the ring), a list of connecting nodes that are respectively connected to the same for an adjacent ring (inter-ring connecting node information), and a list of nodes composing the adjacent ring (topology information of the nodes in the adjacent ring). Based on the information, it is determined whether each of the nodes in the ring is a branch node that branches into a working path and a backup path thereon. If one of the nodes is determined as the branch node, selectable routes between the branch node and an end node on which the working path is terminated in the adjacent ring are determined as a prospective backup path unconditionally. The prospective backup path which has a shortest route is set as the backup path.
In the technique disclosed in Japanese Patent Application No. 2005-209961, the selectable routes between the branch node and the end node are determined as the prospective backup path unconditionally based on the inter-ring connecting node information or the topology information of the nodes in the adjacent ring. Thus, on the network in which two rings are connected via multiple connection paths, the backup path can be set at the same time when the working path through the two rings is set by the signaling.
In the technique disclosed in Japanese Patent Application No. 2005-209961, however, on a network in which three or more rings are respectively connected to the adjacent ring by multiple connection paths, a backup path can not be set at the same time when a working path through the three or more rings is set by a signaling.
Namely, in the technique disclosed in Japanese Patent Application No. 2005-209961, selectable routes addressed to the end node on which the working path is terminated thereon in the adjacent ring are unconditionally determined as the prospective backup path based on the topology information of the nodes in the ring, the inter-ring connecting node information, and the topology information of the nodes in the adjacent ring. Thus, in the case of the network in which three or more rings are respectively connected to the adjacent ring by multiple connection paths, the prospective backup path can not be determined at the same time when the working path through the three or more rings is set by the signaling.
Thus, there is a need of a technology with which it is possible to set, in a multiple-ring network, a working path and a backup path at the same time.